 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.ui.internal.texteditor.quickdiff.compare.equivalence;

 import java.util.ArrayList ;
 import java.util.Arrays ;
 import java.util.Collections ;
 import java.util.ConcurrentModificationException ;

 import org.eclipse.core.runtime.Assert;

 import org.eclipse.jface.text.BadLocationException;
 import org.eclipse.jface.text.DocumentEvent;
 import org.eclipse.jface.text.IDocument;
 import org.eclipse.jface.text.IRegion;

 /**
  * @since 3.2
  */
 public final class DocumentEquivalenceClass {

     private static final boolean DEBUG= false;
     
     private final ArrayList fHashes;
     private IDocument fDocument;
     private final IHashFunction fHashFunction;
     
     public DocumentEquivalenceClass(IDocument document) {
         this(document, new DJBHashFunction());
     }
     
     public DocumentEquivalenceClass(IDocument document, IHashFunction hashFunction) {
         fDocument= document;
         Object [] nulls= new Object [fDocument.getNumberOfLines()];
         fHashes= new ArrayList (Arrays.asList(nulls));

         if (hashFunction == null)
             throw new NullPointerException ("hashFunction"); //$NON-NLS-1$
 fHashFunction= hashFunction;
     }
     
     /**
      * Returns the equivalence hash for line <code>line</code>.
      *
      * @param line the line for which to get the equivalent hash
      * @return the hash in the equivalence class defined by the hash
      * function
      * @throws IndexOutOfBoundsException if <code>line</code> is not a
      * legal document line
      * @throws ConcurrentModificationException if the document is
      * modified concurrently to this method call
      */
     public Hash getHash(int line) {
         try {
             return internalGetHash(line);
         } catch (BadLocationException x) {
             throw new ConcurrentModificationException ();
         }
     }

     private Hash internalGetHash(int line) throws BadLocationException {
         Hash hash= (Hash) fHashes.get(line);
         if (hash == null) {
             if (fDocument == null)
                 throw new AssertionError ("hash cannot be null after loadAndForget"); //$NON-NLS-1$

             IRegion lineRegion= fDocument.getLineInformation(line);
             String lineContents= fDocument.get(lineRegion.getOffset(), lineRegion.getLength());
             hash= fHashFunction.computeHash(lineContents);
             fHashes.set(line, hash);
         }
         
         return hash;
     }

     /**
      * Cleanses the lines affected by the document event from the
      * internal hash cache. Must be called before the document is
      * modified (in documentAboutToBeChanged).
      *
      * @param event the document event
      */
     public void update(DocumentEvent event) {
         if (fDocument == null)
             throw new IllegalStateException ("update must not be called after loadAndForget"); //$NON-NLS-1$
 try {
             internalUpdate(event);
         } catch (BadLocationException x) {
             throw new ConcurrentModificationException ();
         }
     }
     
     private void internalUpdate(DocumentEvent event) throws BadLocationException {
         int linesBefore= fDocument.getNumberOfLines(event.getOffset(), event.getLength());
         String text= event.getText();
         int linesAfter= (text == null ? 0 : fDocument.computeNumberOfLines(text)) + 1;
         int firstLine= fDocument.getLineOfOffset(event.getOffset());
         
         int delta= linesAfter - linesBefore;
         int changed= Math.min(linesAfter, linesBefore);
         
         if (delta > 0) {
             Object [] nulls= new Object [delta];
             fHashes.addAll(firstLine + changed, Arrays.asList(nulls));
         } else if (delta < 0) {
             fHashes.subList(firstLine, firstLine - delta).clear();
         }
         Collections.fill(fHashes.subList(firstLine, firstLine + changed), null);
     }

     /**
      * @return the number of items
      */
     public int getCount() {
         return fHashes.size();
     }

     public void setDocument(IDocument document) {
         Assert.isNotNull(document);
         if (DEBUG)
             Assert.isTrue(document.get().equals(fDocument.get()));
         fDocument= document;
     }

     /**
      * Computes all hashes and forgets the document. Don't call update
      * afterwards.
      */
     public void loadAndForget() {
         int count= getCount();
         for (int line= 0; line < count; line++)
             getHash(line);
         
         fDocument= null;
     }
 }

